1. Field of the Invention
The present invention generally relates to a flat bed reader for electro-optically reading indicia associated with objects passing through the reader and, more particularly, to generating a scan pattern over multiple surfaces of each object to insure reliable reading of the associated indicia.
2. Description of the Related Art
Flat bed laser readers, also known as horizontal slot scanners, have been used to electro-optically read bar code symbols, particularly of the Universal Product Code (UPC) type, at a point-of-transaction workstation in supermarkets, warehouse clubs, department stores, and other kinds of retailers for many years. As exemplified by U.S. Pat. No. 5,059,779; No. 5,124,539 and No. 5,200,599, a single, horizontal window is set flush with, and built into, a horizontal countertop of the workstation. Products to be purchased bear an identifying symbol and are slid across the horizontal window through which a multitude of scan lines is projected in a generally upwards direction.
The symbol itself may be oriented relative to the window in any orientation, for example, a so-called “picket fence” orientation in which the elongated parallel bars of the symbol are vertical, or a so-called “ladder” orientation in which the bars are horizontal, or an inclined orientation in which the bars are inclined at an angle relative to the vertical and the horizontal. The symbol may also be located anywhere on the product, for example, on a bottom surface facing the window, or on any upright surface generally perpendicular to the window, or on a top surface generally parallel to the window. In order for the symbol to be read, at least one of the scan lines must cross over the symbol in a direction generally perpendicular to the bars of the symbol regardless of the orientation of the symbol relative to the window or the location of the symbol relative to the product.
Typically, a rotary mirrored component is rotated underneath the window of the horizontal slot scanner and scans an incident laser beam across a plurality of stationary mirrors for reflection therefrom through the window as a scan pattern of scan lines designed to sweep a symbol on the bottom surface of the product, or on a leading surface (i.e., the surface facing in the forward direction of advancement of the product through the slot scanner) of the product. An operator is trained to position the symbol on the bottom or leading surfaces of the product during use.
The art has also proposed the addition of a vertical window at the workstation in order to project still more scan lines at the product at additional upright surfaces thereof. These dual-window readers provide high performance and enable many products to be processed rapidly, because they eliminate, to a large extent, the requirement to visually locate the symbol on each product, and to turn each product so that the symbol faces the single window of the horizontal slot scanner. All the operator must do is hold the product such that his on her hand is not covering the symbol.
As advantageous as the dual-window readers are, their large size and high cost make them unsuitable for applications where there is insufficient room available to accommodate the extra window, and where the high cost is unjustified. Nevertheless, even small workstations can benefit from a more productive reader which reduces the time that customers must wait for transactions to be processed, and which reduces the number of operators to be hired to provide acceptable checkout service.